1. Field of the Invention
The present invention relates to a shock absorbing system for the front fork of two-wheeled vehicles, especially bicycles. More specifically, the present invention relates to such a shock absorbing system having a hydraulic shock damping unit with variable and adjustable damping characteristics.
2. Description of Related Art
Front fork suspensions have been known for motorcycles for a long time and with the invention of Turner U.S. Pat. No. 4,971,344, became practical for use on bicycles, and have since found widespread use, particularly on mountain bicycles. In the suspension of the Turner patent, air pressure is used to adjust the hydraulic fork to compensate for rider weight variations or to produce a firmer or softer ride. However, because the extension damping performance of the suspension is directly related to the amount of air pressure in the system, adjusting of the air pressure to compensate for a rider's weight could adversely affect the extension damping characteristics of the suspension, and no other means existed to vary the performance characteristics of the suspension, nor was the suspension designed to produce differing performance characteristics under different loading conditions apart from an ability to "lockout" low level forces of the type produced by pedaling while allowing the fork to react to high impact forces.
In Turner U.S. Pat. No. 5,186,481, the fork suspension of the above-mentioned Turner patent was improved to enable varying of the preload on a coil-type compression spring, that acts to hold a compression valve plate of a metering valve located between upper and lower hydraulic chambers in a closed position until a predetermined force level is reached at which time it pops open to allow flow through the valve. In particular, by turning of an adjustment rod so as to screw it more or less into the metering valve, the coil-type compression spring is caused to contract or expand, thereby changing the force required to open the compression metering valve, and allowing a wide range of adjustments for adapting the suspension to widely differing circumstances of rider weight and riding experience. However, this adjustability does not affect the suspension beyond setting the threshold level at which compression of the fork will commence.
Other shock absorbing bicycle forks have since been developed which allow for personalized adjustment of the performance characteristics of the fork. For example, Wilson et al. Pat. No. 5,269,549, discloses a suspension for the front wheel of bicycles in which a spring action is used for shock absorbing purposes and is obtained by a skewered arrangement of stacked elastomeric pads which are disposed between the ends of the fork strut tubes to absorb shocks by deformation thereof. By using different combinations of pads of different durometers, resilience characteristics and/or lengths, the shock absorbing characteristics can be changed in accordance with the rider's weight and the conditions under which the bicycle will be ridden. However, such an arrangement necessitates maintaining a large number of pads and trial and error attempts to achieve the proper performance characteristics taking into consideration the rider's weight, assuming such can be achieved given the combinations of available different pads. Also, an elastomeric suspension simply is incapable of achieving the same kind of ride as a hydraulic suspension in that spring shock absorbing characteristics are a function of the distance they are compressed while a hydraulic suspension has a damping characteristic that is a function of the speed at which the shock absorber is compressed.
Chen U.S. Pat. No. 5,284,352 discloses a compression-adjustable bicycle shock absorbing front fork which, like that of Wilson et al., utilizes a skewered arrangement of interchangeable stacked elastomeric pads, and to which a compression coil spring is added. In addition to the adjustability afforded by the ability to change elastomeric pads, the initial compression characteristics and the travel length which the strut can be compressed can be adjusted by rotating of a mounting member which acts to reduce or expand the initial height of the stacked pads and spring. While an improvement over the Wilson et al. suspension in that adjustments can be made without replacing one or more elastomeric pads with others, it still lacks the damping characteristics of a hydraulic suspension.
Of course, hydraulic shock absorbers with variable damping characteristics are well known in the automotive and motorcycle field. Examples of such variable damping hydraulic shock absorbers can be found in Van Zeggeren U.S. Pat. No. 5,184,703 and in Yamaoka et at. U.S. Pat. No. 5,277,283. In both of these examples, a plurality of flow orifices are provided to provide a plurality of possible flow paths of differing damping characteristics with means being provided to change the orifices/flow paths for the hydraulic damping fluid to vary the damping characteristics. In the case of the Van Zeggeren patent, the variation in damping characteristic is produced electronically, and can be locked into one of two positions, i.e., a "sport" setting having a high damping action and a normal setting providing a softer ride due to a low damping action, or damping can be adjusted in response to various driving condition sensors, such as accelerometers, gradient detectors, etc. Such a suspension is clearly impractical for use on bicycles, even without regard to the fact that motor vehicular suspensions are designed for different purposes than those for bicycle, such as achieving a soft ride while handling vehicular momentum.
The Yamaoka et al. patent seeks to provide stability and comfort during any automotive vehicular driving condition by linearly varying the damping characteristics or damping force of their shock absorber as a function of piston stroke. This result is achieved utilizing a tandem arrangement of orifices having different flow restriction variation characteristics, so that the damping characteristics will vary as a function of piston speed. However, such a motor vehicular suspension also is not designed for bicycle riding conditions, on the one hand, being too costly a construction to be commercially feasible to use on a bicycle, and on the other hand, not providing optimum response characteristics for a bicycle which will be ridden under off-road conditions as well as on and which should not bounce around simply due to pedalling, especially that type of pedalling known as "jamming", not to mention the need for the suspension to be personalized to the rider's weight and riding style.
Thus, there is still a need for a shock absorbing system having a hydraulic shock damping unit with variable and adjustable damping characteristics that will allow a wide range of adjustments for adapting the suspension to widely differing circumstances of rider weight and riding experience, yet, at the same time being practical and economic for use on bicycles by the average rider thereof.